A semiconductor device includes a heater element and a pair of heat sinks disposed on both sides of the heater element. The heater element and the heat sinks are sealed with resin, i.e., they are molded with a resin mold. A heat radiation surface of each heat sink is exposed from the resin mold.
The heat sinks are composed of the first heat sink and the second heat sink. The first heat sink is disposed on one side of the heater element, and thermally connects to the heater element. The second heat sink is disposed on the other side of the heater element, and thermally connects to the heater element. This construction is defined as a both sides heat sink construction.
The semiconductor device having the both sides heat sink construction is disclosed in Japanese Patent Application Publications No. 2001-267469 and No. 2002-110893 (which corresponds to U.S. Pat. No. 6,693,350). The device is manufactured by a transfer mold method as follows. A pair of heat sinks is mounted on both sides of the heater element, and the heater element with the heat sinks is mounted in a mold, i.e., a die. Then, resin is molded into the die so that the device is formed.
In the both sides heat sink construction, heat generated in the heater element is radiated from both sides of the heater element through the heat sinks, so that heat radiation characteristic of the device is improved. Here, the heat sinks have heat radiation surfaces, which are exposed from the resin mold. However, an assembling error of the heat sinks or a slant of the surface of the heat sinks may prevent the heat radiation surface from exposing outside sufficiently. For example, the heat sink disposed on the upper side of the heater element is tilted from the surface of the device so that the heat radiation surface is not sufficiently exposed from the resin mold. Specifically, the heat radiation surface may be covered with the resin mold.
In view of the problem, in prior, the heat sink includes a deformable portion, which is disposed outer periphery of the device. When the heater element and the heat sinks are molded with the resin mold by using a die, i.e., a mold, the deformable portion is deformed so that the heat radiation surface is attached to the mold. Thus, no clearance is formed between the heat radiation surface and the mold so that the resin mold is prevented from inserting into the clearance. Accordingly, the heat radiation surface is sufficiently exposed from the resin mold. However, when the heat sink is pressed and inserted into the mold, the pressure is concentrated into the deformable portion of the heat sink so that all of the surfaces of the heat sink are not pressurized uniformly. Therefore, a portion of the heat sink, in which the pressure is comparatively applied weakly, may be expanded or deformed by the pressure of the resin mold inserted into the die. This deformation of the heat sink causes to decrease the degree of parallelism between the heat radiation surfaces of the heat sinks so that the clearance maybe formed between the heat radiation surfaces and cooling equipment in a case where the device is attached to the cooling equipment. Thus, cooling performance of the device is reduced.